References are cited throughout the specification. These references in their entirety are incorporated by reference into the specification to more fully describe the state of the art to which it pertains.
Positive and negative control of gene expression by retinoids is mediated by nuclear receptors that are part of a large family of regulatory proteins including the steroid and thyroid hormone receptors, the vitamin D receptor, and the retinoid receptors (RAR). This latter group comprises three retinoic acid (RA) receptors: RAR.alpha., .beta. and .tau., that contain highly conserved DNA and ligand binding domains. In addition a more distantly related receptor, RXR, appears to be activated by a RA metabolite.
Nuclear receptors function as transcriptional activators in the presence of their ligand. RARs, like the thyroid hormone receptors, do not require ligand binding for nuclear localization and specific DNA interaction. Until the subject invention, interaction with specific DNA sequences was thought to be essential for all regulatory functions of nuclear receptors.
Since glucocorticoids and RA are known to repress members of the collagenase family they have promise as therapeutic agents in rheumatoid arthritis where proteinases, such as collagenase and stromelysin, play an important role in joint destruction. Collagenase is the only enzyme known to cleave collagen, a major structural component of bone and cartilage destroyed by the enzyme. Retinoids inhibit the production of collagenase by synovial cells while the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) and the inflammatory mediators interleukin 1 (IL1) and tumor necrosis factor alpha (TNF.alpha.) stimulate collagenase secretion and transcription.
Thus, while the RA and glucocorticoid nuclear receptors are known to repress members of the collagenase family, the mechanism of this repression was not known. A logical presumption was that the repression relates to the receptors known ability to bind DNA. However, the present invention provides the surprising discovery that these nuclear receptors actually inhibit transcription through a protein/protein interaction with AP-1, a protein complex composed of Jun homodimers and Jun/Fos heterodimers. Hence, a major discovery that regulatory function of nuclear receptors are mediated by a mechanism that does not involve direct binding to DNA is provided. This discovery provides a mechanism through which arthritis and cancer can be treated.